Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, 
add spaces in s to construct a sentence where each word is a valid dictionary word. 
Return all such possible sentences.

Note:

The same word in the dictionary may be reused multiple times in the segmentation.
You may assume the dictionary does not contain duplicate words.
Example 1:

Input:
s = "catsanddog"
wordDict = ["cat", "cats", "and", "sand", "dog"]
Output:
[
  "cats and dog",
  "cat sand dog"
]

